1. Field of the Invention
This invention relates to louvered arc chutes, and, in particular, to arc chutes utilized in electric circuit breakers for directing the short circuit blast in a safe direction. Accordingly, it is a general object of this invention to provide new and improved arc chutes of such character.
2. Description of the Prior Art
One prior art type of arc chamber barrier, utilized in electric circuit breakers, has been a fine mesh screen. Disadvantageously, the fine mesh screen did not influence the direction of arc supporting vapors, gases and particles being expelled from the arc chamber of the circuit breaker. Further, during a severe short circuit, there was a tendency for the fine wires of the screen to melt and blow out into a metal circuit breaker enclosure, thereby increasing the likelihood of arcing between the line terminal and the enclosure.
Other prior art arc chutes utilize a plurality of arc plate grids, in addition to a screen barrier. Disadvantageously, multiple parts increase assembly labor and material costs.
3. Statement Pursuant to 37 CFR 1.56
The following United States patents may be material to the examination of the application. Though these patents were called to the attention of the applicant as a result of a routine novelty search, no conclusion is asserted that such search was one hundred percent effective, or that no better art exists.
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 2,460,118 Bennett Jan. 25, 1949 2,524,287 Ellis Oct. 3, 1950 2,632,827 Rypinski Mar. 24, 1953 2,898,427 Nadeau Aug. 4, 1959 ______________________________________
Bennett, U.S. Pat. No. 2,460,118, discloses an open type arc chute including two spaced plates of electrically insulating material, shaped to provide a converging arc discharging channel at the top. The two plates are held within a U-shaped magnetic member having upwardly offset flanged portions that embrace the outer faces thereof. At low altitudes (in aircraft where the apparatus is located), an arc is rapidly distended and unable to escape from the converging discharging channel, until it has sufficiently cooled to be rapidly extinguished in the vicinity of the throat of the channel. At high altitudes, where the arc is sluggish, strong magnetic action tends to keep the arc moving, and the cross section of the arc is reduced by the magnetic action which drives the arc into the converging channel where it is cooled sufficiently to be interrupted. No mention is made by Bennett of the burning attributes of the arc chute, including the insulating plates thereof. It is noted that neither the construction nor the function of Bennett is similar to, nor suggestive of, the louvered arc chute of this instant invention.
Ellis, U.S. Pat. No. 2,524,287, discloses an arc extinguishing structure in the form of a conductive or magnetic cup, such that an arc, when drawn, is directed generally thereinto as a result of the magnetic field produced by the current or arc path and the cup. The shape of the cup and the contact relation are such that the magnetic field is always inward towards the bottom of the cup, thus confining the arc to the inside of the cup until extinction occurs. Thus, the arc is prevented from burning or forming conductive particles on the surfaces of insulative materials, which might lead to tracking and dielectric breakdown. However, the cup-shape configuration of Ellis is structurally and effectively different from the louvered arc chute of the instant invention.
Rypinski, U.S. Pat. No. 2,632,827, discloses a device for minimizing the effects of arcs formed on breaking an electric circuit, such, for example, as a switch or circuit breaker. The device is an arc-quenching housing consisting of magnetic metal having four side walls and an end wall, confining the contacts both in the contacting and separated positions. A vent opening through one wall of the housing is spaced from the separation point of the contacts. The housing confines the flame and the molten metal resulting from an arc formed on the separation of the contacts.
Nadeau, U.S. Pat. No. 2,898,427, discloses a one-piece arc extinguishing means comprising a generally U-shaped member of magnetic metallic material having side portions disposed on either side of the path of a movable contact, and extending completely between the contact closed and the contact open positions of the movable contact, the bight portion thereof extending parallel to the path of movement of the movable contact and being provided with a plurality of parallel slots extending generally perpendicular to the path of movement of the movable contact, the slots also being extended into the opposite side portions. In contradistinction, the louvered arc chute of the instant invention provides slots that extend into, and are continuous through, a louvered bight portion from both sides. The unique louvered improvement on the slots provides directional venting with additional cooling surfaces, and a protecting barrier to prevent undesirable elements from being introduced into the circuit breaker mechanism. Integral mounting features of the louvered arc chute hold and position the chute within the molded case housing so that the "U" shaped channel is spaced away from the housing walls, thereby exposing the outside surfaces of the sides of the "U" shaped channel, as well as the housing walls, to hot particles and gases created by a short circuit arc drawn between the contacts. Further, the integral louvered arc chute is mountable in a prior art type molded housing that was designed to receive a "high performance arc stack" consisting of a plurality of arc plates (grids) and retainer liner, a versatility that permits construction of circuit breakers with a common housing that is able to perform under relatively high magnitude fault conditions as well as conventional normal fault conditions.